Abstract
Depletion of groundwater resources has been identified in numerous global aquifers, suggesting that extractions have exceeded natural recharge rates in critically important global freshwater supplies. Groundwater depletion has been ascribed to groundwater pumping, often ignoring influences of direct and indirect consequences of climate variability. Here, we explore relations between natural and human drivers and spatiotemporal changes in groundwater storage derived from the Gravity Recovery and Climate Experiment (GRACE) satellites using regression procedures and dominance analysis. Changes in groundwater storage are found to be influenced by direct climate variability, whereby groundwater recharge and precipitation exhibited greater influence as compared to groundwater pumping. Weak influence of groundwater pumping may be explained, in part, by quasi-equilibrium aquifer conditions that occur after “long-time” pumping, while precipitation and groundwater recharge records capture groundwater responses linked to climate-induced groundwater depletion. Evaluating groundwater response to climate variability is critical given the reliance of groundwater resources to satisfy water demands and impending changes in climate variability that may threaten future water availability.
Highlights
Remote sensing of global groundwater storage changes, with the launch of the Gravity Recovery and Climate Experiment (GRACE) satellites, has enabled important contributions to our understanding of global groundwater[1,17]
Trends in groundwater storage (Fig. 2) correspond spatially to regions of high groundwater pumping (See Supplemental), results depicted in Fig. 4 suggest that complex groundwater processes associated with long-term groundwater pumping may fail to be captured by GRACE
An assumption that groundwater pumping would result in an immediate change in storage is prescribed in Fig. 4, where in reality, changes in groundwater storage due to pumping depends on a variety of physical hydrogeologic characteristics, aquifer geometry and groundwater/ surface water interactions
Summary
Remote sensing of global groundwater storage changes, with the launch of the Gravity Recovery and Climate Experiment (GRACE) satellites, has enabled important contributions to our understanding of global groundwater[1,17]. Changes in groundwater storage may be isolated employing water balance methods whereby terrestrial water storage changes result due to changes in soil moisture, snow water, and surface water stores (See Methods and Data) In this evaluation, changes in groundwater storage for the contiguous U.S are characterized by isolating a representative groundwater storage signal from GRACE. Assessments of GRACE-derived groundwater storage changes have focused on single aquifer[4,5,19,20] or large global aquifer systems[7,21] Often, these studies characterize changes in groundwater storage as a single metric, typically the slope of groundwater storage change over time[5,6,22,23,24], which fails to capture direct and indirect links between groundwater and climate[15]. MLR permits application of dominance analysis, which is used to determine whether an explanatory variable is dominant over another, referred to here as strong (dominant over) or weak (not dominant over) influence
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